The Legislative Council's environmental affairs panel approved an amendment in Air Pollution Control (Emission Reduction Device for Vehicles) Regulation Tuesday to restrict particulate emissions of heavy diesel vehicles.

At present, the regulation requires all pre-Euro standard light diesel vehicles to be installed with approved emission-reduction devices.

The amendment extends the requirement to all heavy diesel vehicles to install the device, except for those that require long idling times, such as concrete-mixing trucks, with effect from the beginning of April.

A voluntary program to install particulate removal devices in heavy diesel vehicles weighing more than four tonnes was implemented last year, and about 97 percent of Hong Kong's 30,000 such vehicles participated in the scheme.

Franchised bus companies retrofitted about 1,400 vehicles with catalytic converters at their own cost. These remove pollutants from the exhaust by reducing or oxidizing them. The amount of particulates emitted by diesel vehicles in the urban area each day has been reduced by about 30 percent since the retrofit.

The cost of installing a catalytic converter depends on the engine size. It costs HK$5,000 for a four liter engine and HK$18,000 for a 15 liter engine.

The Environmental Protection Department records show particulate emissions have been reduced by 76 percent compared with 1997 levels.

The department's target is to achieve an 80 percent reduction by the end of this year.

An EDP official said catalytic converters are just one of the many possible solutions.

Green groups said source control would be much more effective than an ``end-of-pipe'' solution.

Friends of Earth (HK) assistant director Edwin Lau said that pre-Euro diesel vehicles should be replaced by the those that meet the Euro III emission standard.

That standard was introduced in 1999 and is due to be replaced by the Euro IV standard later this year.

He said the government should subsidize vehicle owners to get new Euro III-standard vehicles.

``Franchised bus companies should act responsibly and do something to clean up their emissions,'' said Lau,

who also urged drivers not to use illegal diesel.

``Drivers should fuel up with ultra-low sulfur diesel at Hong Kong petrol stations,'' he said.

``I hope the government can do something to monitor cross-boundary vehicles that use mainland diesel, which is not environmentally friendly.''

University of Hong Kong community medicine chair professor Anthony Hedley

warned that young people and the elderly are particularly sensitive to particulate emissions.